What does it mean when a recipe says to cook something until it is "thick enough to coat a spoon"?

--Angie

The term to "coat a spoon" refers to a simple test to determine when a sauce or custard has thickened enough to use.  As the liquid thickens, it becomes less and less runny.  At some point, if you dip a spoon into the liquid, it will cling to the spoon rather than run off.  The standard technique is to run your finger through the sauce on the back of the spoon.  If a fairly straight line of exposed metal or wood, depending on the spoon, remains visible then the product has thickened to the desired degree.  If the liquid flows back across the line, then it needs to be cooked some more.

Remember when making custards to continue to stir the product off heat for a while once it is done to avoid having the liquid at the bottom become over-cooked from the residual heat in the pan.